1. Field
Transition from analog broadcast to digital broadcast, such as BS digital broadcast, ground wave digital broadcast, is currently in progress.
The embodiments discussed herein are directed to a transcoding device, re-encoder (transcoder), decoder, and transcoding method, in which after encoded image data read from a digital broadcast signal or a storage device is decoded, it is re-encoded, which may include a re-encoding (transcoding) technique for reducing an error included in a decoded image.
2. Description of the Related Art
In a digital broadcast, a compression system that utilizes a correlation between images, such as MPEG2, is used as the motion image compression format. Currently, during a digital broadcast, data is transmitted at ten and some Mbs to twenty and some Mbs. A storage device, such as an HDD recorder, stores the digital data of the digital broadcast signal as is or stores it by re-encoding (transcoding) the image decoded so that the compression rate is increased after decoding the digital data of the digital broadcast signal, i.e., it stores it after reducing the amount of data by encoding again with a lower bit rate than the bit rate of the original image. Reduction in the amount of data leads to an increase in the length of recording time if an HDD recorder has the same capacity.
FIG. 1 is a diagram showing a configuration of such a transcoding device 1. As shown schematically, transcoding device 1 has a decoder 2 that receives and decodes an input data stream encoded in a first format and an encoder (transcoder) 3 that re-encodes (transcodes) data decoded by decoder 2 into a second format and outputs an output data stream. The first encoding format and the second encoding format may be any format, respectively. However, MPEG2 is widely used for the first encoding format and H.264 for the second encoding format, etc. There may be a case where the first and second encoding formats are both MPEG2 and data is transcoded so that the compression rate is increased.
There may be a case where the entire transcoding device 1 in FIG. 1 is put into an LSI, or a case where decoder 2 and encoder (transcoder) 3 are constituted by different LSIs, respectively, or a case where a primary storage device, such as DRAM, is added.
If the amount of data is reduced, the quality of the image degrades; however, an attempt has been made to make the degradation less remarkable by reducing the image size or processing to dull the edge of the image by filtering before re-encoding the decoded image. However, the degradation of the image and length of recording time is a tradeoff.
A transcoding device is described in the following documents.
WO95/2868A describes a device that transcodes a received video stream with a fixed bit rate into a variable bit stream and also hides errors.
JP2002-10261A2 (US2001053182A1) describes that a transcoder control part, which monitors a decoder, controls a transcoder, and controls an encoder, controls an amount of operations of a rate control part and a motion guarantee prediction part so that the amount of code in a buffer and the total number of operations are constant in accordance with the amount of code in the buffer and the amount of operations per unit block.
JP2002-27465A2 describes that a VOP (video object plane) target code amount calculation part which calculates an amount of target code of a VOP is provided and an MPEG4 image information encoding part (I/P-VOP) controls the amount of code in accordance with the amount of target code when encoding image information into MPEG4 image compression information (bit stream).